Modern electronic products using, for example, semiconductor technology, are sensitive to high electric fields and currents, even though such fields and currents may be of a transitory nature. Degradation of performance or permanent damage to the devices is known to commonly occur unless the devices and products are properly protected during the course of production, storage, shipment, installation and use. For storage and shipment, various products, which may be termed ESD (electrostatic discharge) protective packaging, are used to minimize the possibility of damage. They may be used to wrap or bag the product, and may also include containers suitable for handling during typical factory or shipping operations.
ESD protective packaging typically has a characteristic that the surface or volume resistivity of at least a layer thereof is significantly lower than that exhibited by insulators which may be typical plastics, which may also comprise part of the packaging. The lower resistivity may be achieved, or example, by the use of special polymers, the loading of polymers with conductive materials such as metal or carbon, or the deposition of thin layers of metal on plastic. Often a combination of these techniques is used to minimize voltage build up due to triboelectric charging, or to shield the product from high electromagnetic fields or currents.
Identification of products and other items can be performed by the reading of bar codes using optical means and by the use of radio-frequency identification (RFID) to obtain information about a product using a non-contact automated technique. Such information may be used to sort products, inventory the products, retrieve products from storage or similar industrial uses. In particular, RFID is used to interrogate a device, often called a transponder or “tag” that has been affixed to the product or the package. A variety of different frequencies are used by RFID equipment depending on governmental regulations and may include operation in the LF, HF, UHF and microwave frequency ranges. LF and HF operation in the worldwide ISM (industrial, scientific and medical) allocations may be of an unlicensed type, with restrictions on the power used by the interrogating devices.
Items returned to a manufacturer or distributor may have RFID tags, and may also be protected by ESD bags or wrapping. It would be desirable to read the RFID tag without opening the box or container or the ESD bag in which the item was shipped.
When a passive RFID tag is used, the power required to operate the tag is provided by the electromagnetic fields generated and emitted by an antenna associated with the interrogation device. As such, any excess loss of power during the transit of an electromagnetic signal between the interrogation device and the tag will reduce the distance over which the interrogation of the RFID tag can be performed. Since many of the passive RFID tag systems are effective for a range of about a meter or less under ideal conditions, any substantial loss of signal strength may render the entire approach inoperative.
In particular, many types of ESD packaging, having layers of material which enclose the product and which may be conductive, will produce a shielding effect, sometimes known as a Faraday cage, and substantially attenuate the electric and magnetic fields of radiated electromagnetic waves. As such, it may not be possible to interrogate (or “read”) the information on a RFID tag affixed to the product when the product is enclosed in ESD packaging. Even when the ESD packaging partially optically transparent, the reading of bar codes by optical means is difficult. Bar codes on the product would not be readable when the product in an ESD bag is enclosed by an outer shipping container such as a cardboard box.